Selective optical absorption filters for selectively absorbing one or more narrow bands of radiation have found increasingly widespread use with the burgeoning use of lasers in the medical, industrial and scientific fields as well as in other fields. The increased use of various and multiple lasers has increased the possibility of the eye of a viewer or user of such lasers to be subject to dangerous exposure to the laser beam radiation and resulting in damage to the eye. Similarly, optical or light sensitive equipment employed for monitoring industrial or other operations being performed by lasers can also be subject to serious damage due to undesired or prolonged exposure to the radiation of the laser.
Thus, for such purposes, it is necessary to provide transparent optical filters or shields that can be interposed between the source of the radiation, e.g. the laser, and the viewer, e.g. the eye or other optical equipment, for specifically absorbing or filtering to a suitable degree one or more narrow bands of radiation while transmitting radiation to a suitable degree in a broader band surrounding or adjacent the narrow band.
In general such light source filters or shields, useful with various lasers, have been made available by incorporating a suitable light absorbing agent into a suitable matrix or host material. Such filters or shields enable the viewer to see through the transparent shield or filter but protects against damage to the viewer by exposure to undesired radiation from a laser beam. For example, in U.S. Pat. No. 3,853,783, issued Dec. 10, 1984 to Robert Tucker, it is disclosed that a vanadyl phthalocyanine sulfonamide may be incorporated into plastics to provide shields capable of protecting eyes against laser radiation of from about 620 to 720 nanometers. Similarly, in U.S. Pat. No. 3,687,863, issued Aug. 29, 1972 to Paul Wacker, it is disclosed that optical filters may be produced by incorporating metal derivatives of tetraphenylporphines into polymeric matrices. More recently, in U.S. Pat. No. 4,622,174, issued Nov. 11, 1986 to V. McKoy et al, it is disclosed that platinum octaethylporphine can be incorporated in a transparent matrix to absorb laser radiation at 532 nanometers or combined with a vanadyl phthalocyanine for absorption at both 532 and 694 nanometers.
However, many of the previously used absorbing agents produce optical filters of severely limited stability that results in an undesirable loss of optical density. Furthermore, it is found that many of the previously used absorbing agents do not provide sufficiently sharp absorption limits and possess undesirably broad absorption bands. Especially when two or more of such absorption agents are used in combination to protect a viewer against two or more wavelengths of radiation does the undesirable broad absorption bands of the agents represent a significant disadvantage, undesirably limiting transmission of other light available for vision.
Additionally, many of such absorbing agents are insufficiently stable to heat or in-band visible light radiation.
It is therefore highly desirable that absorbing agents be available which overcome one or more of these undesirable side effects and disadvantages of prior absorbing agents and optical filters produced therefrom. It is most desirable that absorbing agents be available for incorporation into suitable matrices for producing optical filters which have sharp narrow bands of absorption and are more stable to heat and in-band visible light. It is also highly desirable to have such absorption materials which can be combined with other absorption materials in suitable matrices for producing optical filters for suitably protecting viewers against two or more wavelengths of laser light.